Recognition of implantable medical device

ABSTRACT

Controlling the interaction between an external device and an implanted device, including a method of controlling interaction between an external device and an implanted device, the method including at least the steps of: establishing communications between the implanted device and the external device; the external device determining an identification of the implant and comparing the identification with identifications in a stored list; if the device matches one of said identifications, then using a corresponding set of operating parameters to interact with said implant; and otherwise, not interacting with said device.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent application No.12/279,055, entitled “RECOGNITION OF IMPLANTABLE MEDICAL DEVICE”, filedon Aug. 11, 2008 which is a National Stage application ofPCT/AU2007/000142 entitled “IMPLANT ID RECOGNITION”, filed on Feb. 9,2007, which claims priority from Australian Provisional PatentApplication No. 2006900628, filed on Feb. 10, 2006, which are herebyincorporated by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to implantable medical devices, and moreparticularly, to recognition of implantable medical devices.

2. Related Art

Implantable hearing prostheses provide the benefit of hearing toindividuals suffering from severe to profound sensorineural hearingloss. Sensorineural hearing loss is due to the absence or destruction ofthe hair cells in the cochlea which transduce acoustic signals intonerve impulses. An implantable hearing prosthesis essentially simulatesthe cochlear hair cells by delivering electrical stimulation to theauditory nerve fibers. This causes the brain to perceive a hearingsensation resembling the natural hearing sensation.

The present invention is particularly concerned with situations where auser, patient or recipient, “recipient” herein has an externalprocessing device that communicates with an implanted device. Forexample, in a modern, conventional cochlear implant, an external speechprocessor transmits power and data to the implanted device via aninductive coil arrangement. The implanted device includes an electrodearray to deliver the desired electrical stimuli to the cochlea of therecipient.

Once implanted, the implant system is typically adjusted to suit thespecific needs of the recipient. As the dynamic range for electricalstimulation is relatively narrow and varies across recipients andelectrodes, there is a need to individually tailor the characteristicsof electrical stimulation for each recipient. This procedure, oftenreferred to as “fitting,” “programming,” “mapping” (“mapping” herein)involves measuring and controlling the amount of electrical currentdelivered to the cochlea. Typically, a clinician, audiologist or othermedical practitioner (generally and collectively referred to as“audiologist” herein) uses interactive software and computer hardware tocreate individualized programs, commands, data, settings, parameters,instructions, and/or other information (generally and collectivelyreferred to as a “MAP” herein) that define the specific characteristicsused to generate the electrical stimulation signals presented to theelectrodes of the implanted electrode assembly. It is increasinglycommon for recipients to have a cochlear implant for each ear, which iscommonly known as bilateral implantation. The advantages of bilateralimplantation vary from recipient to recipient, and may include improvedspeech perception, and the ability to localize sounds. However, due todifferences in the anatomy and physiology of recipients, and in the needto precisely place the electrode array, there will almost always bedifferences in the map between the left and right ears. The recipientwill have two speech processor devices, each operating according to adifferent MAP. The speech processor devices are typically identical inappearance, and may inadvertently be swapped. This is a particular issuefor very young and elderly recipients, as well as those with conditionssuch visual impairment. The use of the incorrect speech processor devicewill at best lead to reduced speech perception, as the incorrect MAP isapplied, and potentially to pain for the recipient as excessivestimulation values are utilized for that ear.

SUMMARY

In a broad form, the present invention provides multiple sets ofoperating parameters (maps or the like) within each external device,each set being associated with an identified implant. Before theexternal device begins to transmit stimulation or other operational datato the implant, it determines the identity of the implant, and then usesthe corresponding set.

According to one aspect, the present invention provides a method ofcontrolling interaction between an external device and an implanteddevice, the method including at least the steps of: establishingcommunications between the implanted device and the external device; theexternal device determining an identification of the implant andcomparing the identification with identifications in a stored list; ifthe device matches one of said identifications, using a correspondingset of operating parameters to interact with said implant; andotherwise, not interacting with said device.

According to another aspect, the present invention provides an externaldevice adapted to interact with an implanted device, the external devicebeing adapted to detect an identification from an implanted device,determine if the identification corresponds to one of a plurality ofidentifications, and if the identification does correspond, utilize astored set of operating parameters corresponding to said identification.

According to another aspect, the present invention provides an externalhearing device adapted to interact with an implanted device, theexternal device being able to be operatively positioned to interact witheither a left ear or right ear implanted device, said external deviceincluding sensor means operatively adapted to detect whether theexternal device is positioned to interact with the left ear or the rightear implanted device, and in response to said sensor utilize a storedset of operating parameters corresponding to the left ear or the rightear implanted device.

The present invention accordingly provides an arrangement whereby, forthe bilateral implantee, it does not matter which SP is selected forwhich ear—both can store the map for each ear, and deliver the correctstimulation instructions for the respective implant. If the implant isnot identified, the SP will not operate. The invention can be applied inany form of implanted device where multiple external devices may beinadvertently associated with the wrong implanted device.

The invention is also applicable to implanted devices where the externaldevice may only be periodically connected, for example, a totallyimplantable auditory prosthesis.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described withreference to the accompanying figures, in which:

FIG. 1 illustrates schematically a bilateral implant situation;

FIG. 2 is a conceptual block diagram of the operation of oneimplementation of the present invention;

FIG. 3 is a flowchart illustrating the operation of the requiredsoftware of one implementation;

FIG. 4 illustrates the general operation of a cochlear implant system;

FIG. 5 illustrates the operation of another implementation of theidentification system; and

FIG. 6A and 6B are graphs illustrating how the characterization of apredefined subset of parameters can be used to differentiate between twosimilar implants.

DETAILED DESCRIPTION

The present invention is capable of implementation m any desired type ofimplantable device which interacts with an external device. For example,the present invention may be used in conjunction with any acoustic orelectrical auditory device, such as a middle ear implant, intracochleararray implant, brain stem implant, implanted acoustic device or anycombination, for example combined electrical and acoustic stimulation.The external device may be continuously, intermittently or occasionallyin communication with the implanted device. The present invention mayalso be used in non-auditory applications where a component is implantedand interacts with an external device. However, embodiments of theinvention are described with reference to an embodiment in a cochlearimplant system.

FIG. 1 illustrates conceptually a recipient 10 having an intracochleardevice 11, 12 implanted in each ear 13, 14, respectively. For eachimplant 11, 12, a corresponding external device 17, 18 is required. Theexternal device incorporates one or more microphones, batteries,processor and the necessary software to process sound signals andtransmit them via coils 15, 16 to the implanted device.

A more detailed description of typical external and implant devices of acochlear implant is provided in FIG. 4. It is noted that such devicesare in widespread commercial use, and well understood by those skilledin the art, so that only a general overview of their structure andoperation will be provided. Moreover, various structural variations andalternatives exist, as will be well known to those skilled in the art.

FIG. 4 illustrates an overview of the components of one form ofimplantable hearing prosthesis, a cochlear implant. The externalcomponent of the cochlear implant, generally indicated as 142, includesa behind the ear (BTE) device 116, designed to sit behind the pinna 122.This houses the required electronics and software (not shown), andbatteries to power the external component as well as transfer power tothe implanted device 144. BTE device 116 is connected via a lead 118 tothe antenna transmitter coil 106, which is generally disc shaped andincludes housing 108 for the coil itself (not shown). A magnet 110 isprovided to assist in correctly locating the antenna transmitter coil106 relative to the implanted device, to optimize efficiency of powerand data transfer.

The implanted component 144 includes receiver/stimulator unit 112 andelectrode lead 130. Receiver stimulator unit 112 includes a sealedelectronics package 128, and a coil 124 to receive the RF signals sentfrom transmitter coil 106. There may also be a back transmissionmechanism, to transfer telemetry data to the external device 142. Amagnet 140 provides assistance in alignment of the transmission coil106. Electrode lead 130 passes stimuli to the electrodes 134 fordelivery within the cochlea 132, so as to produce a neural response inauditory nerve 138.

In operation, the electronics within the BTE device 116 convert sounddetected by microphone(s) 120 into a coded signal. The external antennacoil 106 transmits the coded signals, together with power, to thereceiver/stimulator unit 112 via a radio frequency (RF) link.

Once implanted, the parameters for stimulation are typically adjusted tosuit the specific needs of the recipient. As the dynamic range forelectrical stimulation is relatively narrow and varies across recipientsand electrodes, there is a need to individually tailor thecharacteristics of electrical stimulation for each recipient. Audiologymeasurements may be used to establish the useful range for eachelectrode, and such parameters can be stored within the recipient's BTEdevice 116 for continual use. As noted, this procedure is often referredto as “mapping” and is the term commonly given to the process ofmeasuring and controlling the amount of electrical current delivered toeach electrode, as well as selecting which electrodes to stimulatecorresponding to the respective sound signal. Other operational issueswhich may differ between ears include the speech processing strategy orparameters of that strategy, when to switch between differentstrategies, and other functions and parameters. Different “MAPS” may beapplied in different situations/environments such as home, car,classroom, theatre etc, so each external device may store many maps. Itwill be appreciated that the present invention is applicable to theselection of all such functions and parameters as may be customizablefor each patient or implant according to the particular requirements andoptions of the implant and external device in question.

Importantly for the present invention, the MAP for each implant willdiffer due to variations in the patient's anatomy and physiology, and inthe precise placement of the electrode array, there will almost alwaysbe differences in the MAP between the left and right ears.

FIG. 2 illustrates one implementation of the present invention.Microphone(s) 120 receives ambient sound signals which are thenprocessed by a digital signal processor (DSP) 31. The signals areprocessed according to any one of the known speech processing strategiesto produce a set of signals which are intended as the basis forstimulation. The signals are then converted into specific sets ofstimuli for specific electrodes at specific times and for specificamplitudes. The set of MAPS (that is, the MAPS corresponding todifferent environments) for the appropriate implanted component 144 isrequired to perform this process. According to this implementation,multiple sets of MAPS are stored, each set of MAPS corresponding to aparticular implant identifier. Embodiments of the implant identifier aredescribed in further detail below. Module 33 selects the appropriateMAP, and other parameters as required, based on the implant IDidentified by module 33. Once the stimuli have been determined, theappropriate coded signals are transmitted via the bidirectionalcommunications interface 34 to interface 44 of implanted component 144.From the perspective of implanted component 144, it is not necessary tochange the mode of operation. The receiver/stimulator 41 receives thesignal, converts it to a set of stimuli, for example using an optionaldigital signal processor (DSP) 42, and sends the stimuli to electrodes134.

Implanted component 144 may contain a module to provide the require IDsignal. This may be any arrangement capable of providing an appropriateID signal which is not shared with other implants. It is ideally unique,but need not be. One option would be to send a specific electricalsignal after power up or after detection that the external device is inoperation. This type of ID is used in some commercially availabledevices. Any alternative form of implant identification can be employedwith the present invention.

One alternative would be to provide some form of specific automaticidentification of which side of the recipient's head an external device,such as a BTE device, has been placed. This could be done by the use ofa proximity or thermal sensor such as is shown as reference 200 on FIG.4. In the thermal case, the sensor will operatively either be placednear adjacent the user's head, or facing away, with a substantialdifference in heat This allows the appropriate left or right map to beselected. However, this does not prevent the recipient from using acompletely wrong device, as may occur in a classroom situation.

Another alternative would be to provide a source localization algorithmon the microphone in external device 17, 18. If the device is on theleft ear, most sound will come from the right side and vice versaallowing determination of which ear the device has been placed andtherefore allowing the appropriate selection of left or right map.

If no sensor is working and the implanted component is one that cannottransmit internal voltages, external device 17, 18 may still have MAPSfor the left and right which the recipient 10 may select themselves, forexample by pressing a selection button at start-up.

An approach suitable for use for an implant which has not been designedto produce a specific ID signal will be described with reference toFIGS. 5 and 6. The general approach is in principle applicable to anyimplant which is capable of sending the required parameters via atelemetry system to the external device. The principle of this approachis that each device has internal operating values that vary from deviceto device. The present example uses certain internal voltages which canbe output using existing telemetry arrangements, and which as astatistical measure allow for accurate identification of particularimplants. However, any suitable subset of internal parameters could beused as may be appropriate for a particular implant device.

FIG. 5 illustrates the statistical basis used. In any real system,manufacturing variations result in various parameters having a normallydistributed range of values about a nominal value. The parameters arerequired to fall within minimum and maximum ranges to be acceptable froma quality perspective. However, some of these values are relativelyconstant over time, and are a specific value of that parameter for theparticular implant. When a number of these parameters are consideredseparately, then if there is a sufficient overall match, the implant canbe sufficiently identified.

The choice of the suitable subset of parameters for use in deviceidentification will depend on device design and the normal variance ofthe parameters. Most active implantable devices have a range of internalparameters that may be suitable, such as regulated supply voltages,reference voltages and programmable currents.

For example, referring to FIGS. 6A and 6B, the following parametersmight be selected:

-   -   Parameter 1 =Regulated analogue supply voltage (Vdda)    -   Parameter 2 =Regulated digital supply voltage (Vddd)    -   Parameter 3 =Reference voltage (Vref)    -   Parameter 4 =Voltage measured across internal load for stimulus        level A1    -   Parameter 5 =Voltage measured across internal load for stimulus        level A2, where the value of the internal load resistor and the        two current levels A1 and A2 will vary between implants.    -   Parameters 6 to 10 =Parameters 1 to 5 but measured using a        different voltage measurement range. The gains of the different        measurement ranges will vary between implants, for example due        to the non-linearity of the voltage amplifier in each implant.

Alternatively, other measurements such as the physiological propertiesof the ear, eg some aspect of the neural response with the implant orthe impedance of the electrodes in the cochlea, can be used asparameters for use in device identification.

FIGS. 6A and 6B show the value of various voltages, plotting theparameter value against the parameter. It can be seen that each implanthas a specific signature which is different from other implants, so asto provide a specific identification of a particular implant. It ispossible that another implant could have the set of parameter values,but this is sufficiently unlikely that that the practical risk ofinadvertent connection may be disregarded.

One implant will now be described. For each implant (at the time offirst surgery, or first fitting) the subset of parameters listed aboveis measured and stored as internal ID pattern. To improve thereliability of the measurement the parameters can be averaged, whichalso serves to minimize the statistical variance.

Every time the speech processor is placed on an implant the same subsetof parameters is measured. The ID recognition test passes if and only ifall of the parameters measured lie within, say T*sd of the value of thatparameter in the internal ID pattern. The parameter T is a thresholdthat determines the trade-off between the sensitivity and specificity ofthe test: a large value of T means that we have a very low probabilityof wrongfully rejecting the correct implant (false negative rate), asmall value of T means we have a low probability of wrongfully acceptingthe wrong implant (false positive rate).

The parameter sd in the test criteria is the standard deviation of eachparameter on repetitive measurement on the same implant, which is around0.6 for the Freedom implant. Trials have indicated that T=3.25 providesacceptable false negative and false positive outcomes. It will beunderstood that for each type of implant, different parameters may beappropriate, and different values for T and standard deviation will needto be applied. The standard deviation may be different for differentparameters.

It will be appreciated that this is a process which will differ fordifferent external devices and a suitable set of identificationparameters can be selected as has been described.

In practice, every time the speech processor is switched on stimulationshould be halted until an implant is detected. Also, when a coil-offcondition occurs for longer than 3 seconds, stimulation should haltuntil the implant is detected again. Before starting stimulation (atswitch on, or after coil-off) the test should pass first.

When an implant is (re)detected, the above mentioned parameters aremeasured using 50 averages. This dataset is labelled D(1) . . . D(n).The speech processor should check that for I=1 . . . n:

R(i)+T*sd<T(i)>R(i)−T*sd

When the test passes, stimulation can start. If the test fails, it isrepeated to rule out statistical errors. When after five (5) tests, thetest still fails the speech processor should refrain from stimulatingand give a helper message on the LCD display of the implant.

It may be desirable in some applications that the user be able tooverrule the error and start stimulation by a specific button presscombination to manually select the correct operating program for theimplant.

It will be understood that a different process may be used to implementthe invention if desired, and that alternative processes are likely fordifferent external devices.

FIG. 3 is a flow chart illustrating the process which can be employed inthe BTE device 116 software. It is noted that it would be possible toperform the ID process primarily from the implant itself, however, ingeneral it is preferred to minimise the complexity and processing loadfor the implanted device.

FIG. 3 shows the step 50 by which the identifier is detected. This willobviously differ depending upon the identifier used. Once the identifieris located, at step 51, the appropriate parameters and mode of operationwill be selected, corresponding to the implant identified. It will beappreciated that the exact set of parameters will depend upon the typeof implant, and apart from the map as such, may include other operatingparameters, mode of stimulation, type of speech processing algorithm,and such other parameters as are desired.

It is preferred that the identification process occur as often asrequired to ensure safe operation. This may include, for example, atpower on of the BTE device, or whenever communications between theimplant and BTE are interrupted for more than some predetermined period,for example 3 seconds. In each case, the ID process should be completedbefore stimulation occurs.

Once the parameters are determined at step 51, operation of the devicecan be initiated. At step 53, operation can continue until conditionsrequire the ID to be re-checked, as noted above.

It will be understood that the present invention may be applied toinclude more than two sets of operating parameters. For example, in ahousehold where there are multiple implant users, all the SP devicescould be loaded with the parameters for the implants of everyone in thehouse. This may be of particular benefit with small children. Thepresent invention further provides flexibility for the user. If one SPdevice is not operating, for example due to low battery power, theremaining device can be used for the better ear.

Further features and advantages of the present invention may be found inInternational Application No. PCT/AU2007/000142 entitled “IMPLANT IDRECOGNITION”, filed on Feb. 9, 2007, which claims priority fromAustralian Provisional Patent Application No. 2006900628, filed on Feb.10, 2006, which are hereby incorporated by reference.

It will be appreciated that any other suitable identification processcan be used in accordance with the present invention. Variations andadditions can be readily added as will be apparent to those skilled inthe art.

What is claimed is:
 1. A method for controlling operation of an externaldevice with an implanted internal device, comprising: establishingcommunications between the external device and the internal device;determining, by the external device, at least one identifier of theinternal device; comparing, by the external device, the identifier ofthe internal device to a list of known identifiers to confirm that theinternal device is known; and selecting and utilizing, by the externaldevice, a set of operating parameters stored on the external device, theoperating parameters corresponding to the internal device, and enablingthe external device to operate with the internal device.
 2. The methodof claim 1, wherein the internal device is a stimulator/receiver unit ofa cochlear implant and the external device is a cochlear implant speechprocessor.
 3. The method of claim 1, wherein the operating parametersare selected from the group including one or more of an electrode mapincluding stimulation levels, which electrodes to stimulate, type ofspeech processing strategy or algorithm, parameters of the speechprocessing strategy, or when to switch between different speechprocessing strategies.
 4. The method of claim 1, wherein the identifieris a transmitted identification signal.
 5. The method of claim 1,wherein the identifier is determined from a set of measured parametersrelated to one or more of either the internal device and physiologicalproperties of an ear of a recipient of the implanted internal device. 6.The method according claim 1, wherein the identifier is anidentification tag or device operating independently of the normalcommunication path between the implanted internal device and theexternal device.
 7. The method of claim 1, further comprising: theexternal device displaying a message on a display, said messageindicating at least that the external device is not operating with theinternal device.
 8. The method according to claim 7, further comprising:the external device allowing a recipient to manually select a set ofoperating parameters corresponding to the internal device.
 9. Anexternal device adapted to interact with an implanted internal device,the internal device having at least one identifier, and the externaldevice having a stored set of operating parameters; the external deviceconfigured to detect the identifier from the internal device, determineif the identifier corresponds to one of a plurality of identifiers, andif the identifier does correspond, select and utilize a stored set ofoperating parameters corresponding to said corresponding identifier toallow the external device to operate with the internal device.
 10. Theexternal device of claim 9, wherein the internal device is a cochlearimplant and the external device is a speech processor.
 11. The externaldevice of claim 9, wherein the operating parameters are selected fromthe group including one or more of an electrode map includingstimulation levels, selection of electrodes to stimulate, speechprocessing strategy or algorithm, parameters of the speech processingstrategy, or when to switch between different speech processingstrategies.
 12. The external device of claim 9, wherein the identifieris selected from a set of measured parameters related to one of eitherthe internal device and physiological properties of an ear of arecipient of the implanted internal device.
 13. The external device ofclaim 9, wherein the external device is configured to allow a recipientto manually select a set of operating parameters to be utilized by theexternal device.